Headsets used for two-way communication and audio listening and pure headphones only used for audio listening can be divided into four categories: circumaural, supra-aural, earbud and in-ear headphones.
Circumaural headphones have earpads that encompass the ears. As these headphones completely surround the ear, they can seal very efficiently against external noise.
Supra-aural headphones have earpads that press on the ears, and not around them.
Both circumaural and supra-aural headphones can be provided with open-back earcups or closed-back earcups. The open-back earcups do not block out external noise and audio and leaks audio from the speaker to the surroundings. The closed-back earcups more efficiently blocks out external noise and do not leak audio in any significant amount.
Ear defenders are of a construction similar to the closed-back circumaural headphones, as the main purpose is to block out external noise.
Users of headsets and headphones of the circumaural and supra-aural type and ear defenders often experience discomfort due to build-up of heat in the interface between the earpad and skin of the user. The soft earpad is pressed against the skin of the ear or ear surroundings, and is adapted to the surface whereby heat is more or less prevented from dissipating from the skin. Especially because the earpad normally is a made of foam which has a heat insulating effect. As the earpad often is provided with a cover layer of artificial leather or just soft plastic, air is prevented from cooling the interface between the skin and the earpad. Thus, the ear or ear surroundings may feel warm by the user, whereby he may desire to remove the headset after a short time of use.
Different solutions have been proposed to solve this problem.
U.S. Pat. No. 6,856,690 B (Plantronics) discloses a headset earpad with microcapsules of a material capable of an endothermic phase change at a substantially constant temperature.
U.S. Pat. No. 4,674,134 A (Bilsom AB) discloses an earpad with a sealing ring, which has an outer liquid ring layer, i.e. one intended for engagement against the head, and inwards thereof a foamed plastics ring layer, i.e. towards the juncture with the rest of the earmuff. This ring layer combination s supposed to have good comfort properties while retaining the properties of the sealing ring necessary for sound damping. The liquid layer is supposed to give a “cooling effect”.